1. Field of the Invention
The present invention relates to a projection display apparatus (image display apparatus) such as a liquid crystal projector.
2. Description of the Related Art
Since a polarization characteristic of a polarization beam splitter or a phase compensation plate (phase difference plate) of a projection display apparatus have incident angle dependency, polarized light in the entire incident angle range cannot be uniformly split, but the light partially becomes leaked light. In addition, since normally reflected light (0th order reflected light) and other order diffracted light beams which are generated through reflection of incident light on an image display element (image modulator) are reflected at different angles, the incident light is differently influenced by polarization elements, so that light leakage occurs. Due to the light leakage, a problem occurs in that the contrast of a projection image is deteriorated.
In order to solve this problem, Japanese Patent Laid-Open No. (“JP”) 2011-33762 proposes arranging a phase difference plate having an inclined optical axis between the polarization beam splitter and the image display element. The phase difference plate has different refractive indexes in two orthogonal directions in the optical plane, and a phase difference larger than λ/4 to the polarized light having a designed wavelength λ which vertically enters the optical plane. Assume that a z axis is a normal direction of an incident/emitting plane of the polarization beam splitter, a y axis is a direction perpendicular to the z axis and the normal line of the polarization splitting plane, and an x axis is a direction perpendicular to the z axis and the y axis. Then, the optical axis of the phase difference plate is located on the xz plane and inclines with respect to the x axis. By appropriately setting the angle of the optical axis, the asymmetry generated by the polarization beam splitter can be compensated (cancelled).
JP 2011-33762 uses the uniaxial dielectric crystal such as sapphire or quartz for the phase difference plate, but the uniaxial dielectric crystal is hard to process or handle and has a high sensitivity to the axial angle and a low contrast stability. In other words, when the angle of the optical axis shifts from the designed angle due to the manufacturing error and the installation error, the contrast of the projection image is greatly deteriorated and the contrast cannot be stably improved.